If you want Mechs in scale with with the Armorcast 28mm scale model kits, here is the Mech info from the old Armorcast website:
http://timdp.members.sonic.net/battletech/
Pics:
http://timdp.members.sonic.net/battletech/GamingBattleMech.html
http://timdp.members.sonic.net/battletech/CoolMechs.html
Here are the Robotech Defenders / Macross kits that fit with the Armorcast Mad Cat, Vulture and Atlas resin kits scalewise:
Valkyrie action figures (vinyl) are perfectly sized for Wasps and Stingers.
The Bandai and Arii 1/72 scale plastic model kits, which are a little larger than the vinyl toys, will work for Valkyries and with additonal armor could probably be used as Phoenix Hawks. They also come in transformable versions for the LAM variants.
1/72 scale Armorered Valkyries can probably be used as Crusaders with some modification. I have one to play with but have not had time to work on it.
Takara Dougram and Revell Robotech Defenders Kits These kits were orignally released by Takara as part of their Dougram line. Most of them were later released by Revell in the US ad Robotech Defender kits. Interestingly enough the Takara and Revell kit engineering and mold designs are completely different, with the Revell kits being slightly smaller, but not enough to worry about.
Robotech 1/48 Commando is just the right size for Goliath
Robotech 1/48 Zoltek is perfect for Shadow Hawk
Robotech 1/48 Gartan is a good size for Thunderbolt
Robotech 1/48 Thoren is perfect for Griffin
(This kit is listed as 1/72 scale on the box, but is actually 1/48: 7+" tall)
Robotech 1/48 Talos is too large for Wolverine, but the head could perhaps be mounted on a Griffen body to make a Wolverine.
Robotech 1/48 Condar does not conform to any BattleTech Mechs
Macross 1/72 Glaug Commander's Pod is a perfect size for Marauder
(The more common 1/100 scale kit is too small.)
The ARII 1/72 Defender and Tomahawk (Warhammer, Rifleman) are a bit too small.
Takara Crusher Joe 1/48 Scale Galleon kits a perfect for Galleons.
BattleTech / Macross / Robotech Defender cross reference chart:
BattleTech Macross Robotech Defender
Shadow Hawk Dougram Jagd Zoltek
Griffin Soltic Roundfacer Thoren
Wolverine Blockhead Talos
Thunderbolt Ironfoot Gartan
Battlemaster Bigfoot Ziyon (1/72 scale kit-too small)
Goliath Crab Gunner or Commando Tequila Gunner
Marauder Glaug Commander's Pod
Many of these kits can be found occasionally on ebay (keep watching EVERY week). This is pretty much the only way you can get any of the unseen Mechs in this scale, so get them while (and where) you can.